For all that, if the new-look Giants can play half as well as Jennings has conducted his life since junior year of high school, they might just make it. The former Jacksonville and Oakland runner/pass-catcher almost didn’t get out of the starting gate.

He always wanted to be a running back, but at 270 pounds — “Chubby, dorky, red-rimmed glasses, asthma, everything,” Jennings said — he had played in only one game before junior year in high school. It didn’t help that his grade point average sat at 0.6.

It was during his junior season, while consuming the extra drinks and snacks he and his down-the-depth-chart friend would bring to games, that a University of Tennessee assistant came to scout the starting running back. The starter got hurt. The second-stringer got hurt. They put in a wide receiver and he got hurt.

Left with no other options, Jennings’ coach told the pudgy scrub to grab a helmet. Jennings scored two touchdowns. Then the starting linebacker got hurt. Grab a helmet. He scored two more TDs on defense.

After the game, the Vols’ scout told him he couldn’t help but notice Jennings. It marked the first time someone outside the high school actually projected him for higher things.

Jennings took that and ran with it. He transferred high schools, got his grades up, started eating with nutrition in mind, got into Pitt, transferred to Liberty, and built himself into the Jaguars’ seventh-round pick of 2009.

The kid nobody believed in became one of the Giants’ prime free agent pickups this year, due much to the departures of Andre Brown and Brandon Jacobs and the still-uncertain future of David Wilson. Yet, his life, and how he took ownership of it mirrors much about how the offense has wrapped its arms around McAdoo’s new system of shorter and quicker passes.

For Jennings, who caught 36 passes for the Raiders last year but has never brought one of his 97 career completions into the end zone, it will mean a lot more swings and screens this year. For Manning and his receivers, it will mean shorter routes and faster releases.

And none of them any options other than to believe in the system and be accountable for themselves.

“We just have to conform to it, roll with the punches, and buy into it,” said Victor Cruz, who finds himself the veteran leader of the receiving corps now that Hakeem Nicks has gone off to Indy. “Just do what we have to do.

“I feel good about the offense right now, and feel good about how I feel. The stuff we did in minicamp has carried over.”

The playbook of Jennings’ life wasn’t always a smooth, well-organized narrative. But he has rounded off the ragged edges to reach a point where Coughlin and McAdoo are counting on him to produce. Whatever the role of the running back in this West Coast incarnation turns into, Jennings will be largely responsible for its appearance.

“I don’t write my checks. I don’t make the decisions,” Jennings said. “The only thing I can control is how hard I work. I’ve been that guy since college. That’s where I’m at with it.